The present invention concerns improved hull forms for surface effect ships including a center platform with two side walls (keels), able to operate either as a buoyant displacement vehicle or as an air cushion supported vehicle.
Such a ship is supported by an air cushion confined below the center platform by the two side walls (keels) on the one hand and on the other hand at the stern and the bow by two sealing devices. When the cushion is supplied by the pressurized air, the ship is raised to a position where only the lowest part of these two keels is under water, the air escaping from the cushion only through the two sealing devices. In such a supported position, the ship can sail at high speed (fronde number equal or larger than 1) with the help of propelling systems like propellers or hydrojets. When the cushion is no longer supplied, the seals can be listed and the ship floats over its two side walls (keels), as a buoyant displacement ship.
This type of surface effect ship is well known and is described for instance in French Pat. Nos. 2,422,535, 1,569,807 and U.S. Pat. No. 4,272,779.
Generally, the surface effect ships of the previously mentioned type have been designed and built to operate mainly as air cushion supported vehicles; the buoyant mode is only a secondary mode for sailing at low speed.